To begin with, we consider a high energetic virtual photon \(\gamma ^\ast \)  with four-momentum \(p\)  scattering off a hadronic target, after that, a quark-antiquark pair \(q\bar{q}\)  is produced. This process typically corresponds to quark-antiquark pair (or dijetStrictly speaking, for dijet production, the chanel \(\gamma ^\ast q\rightarrow \gamma ^\ast qg\)  should be included. However, since we are only interest in small-\(x\)  regime, in which the gluon density is very large as compared to the quarks, in this sense, the contributions of quarks can be neglected. Otherwise, the quark part enters and gives an additional contribution to the cross section [1]}, [2]}.) production in DIS via the exchange of a virtual photon. For this process, the hadronic target can be regarded as classical gluon field due to the dominance of gluon saturation effects [3]}, [4]}, [5]}, [6]}, [7]}. Therefore, it is convenient to calculate the cross section in the CGC formalism, the standard way is to consider the virtual photon \(\gamma ^\ast \)  fluctuates into a quark-antiquark pair \(q\bar{q}\) , and then traverse the background field in an eikonal way, simultaneously, the fluctuated quarks receive a contribution to the scattering amplitude with a Wilson line. After averaging over the photon's polarization and summing over the quark's helicities and colors, the differential cross section for this process can be expressed as follow [8]}, [9]},
\(\begin{split}\frac{\mathrm {d}\sigma ^{\gamma ^\ast _{T,L}A\rightarrow q\bar{q}X} }{\mathrm {d}^3k_1 \mathrm {d}^3k_2}=& N_c \alpha _{\text{em}} e^2_q \delta (p^+ - k^+_1 - k^+_2) \int \frac{\mathrm {d}^2{x}_1}{(2\pi )^2} \frac{\mathrm {d}^2{x}^{\prime }_1}{(2\pi )^2}\frac{\mathrm {d}^2{x}_2}{(2\pi )^2} \frac{\mathrm {d}^2{x}^{\prime }_2}{(2\pi )^2} \\& \times e^{-i{k}_{1\perp } \cdot ({x}_1 - {x}^{\prime }_1)} e^{-i{k}_{2\perp } \cdot ({x}_2 - {x}^{\prime }_2)}\sum _{\lambda \alpha \beta } \psi ^{T,L\lambda }_{\alpha \beta }({x}_1 - {x}_2) \psi ^{T,L\lambda \ast }_{\alpha \beta }({x}^{\prime }_1 - {x}^{\prime }_2) \\& \times \left[1 + S^{(4)}_{x_g}({x}_1,{x}_2;{x}^{\prime }_2,{x}^{\prime }_1) - S^{(2)}_{x_g}({x}_1,{x}_2) - S^{(2)}_{x_g}({x}^{\prime }_2,{x}^{\prime }_1)\right]\end{split}\) 
